Circularly polarized broadcast antenna

ABSTRACT

A circularly polarized broadcast antenna comprising a pair of conducting arms having portions forming an interrupted loop polarized in a first plane and terminating in ends diverging in different directions from the first plane to form a dipole.

United States Patent Edward H. Shively Raymond, Maine 04071 652,458

July 11, 1967 Apr. 27, 1971 Inventor Appl. No. Filed Patented CIRCULARLY POLARIZED BROADCAST ANTENNA 10 Claims, 6 Drawing Figs.

11.8. CI 343/704, 343/730, 343/742, 343/743, 343/744 Int. Cl H01q 11/12, l-lOlq 1/00 Field of Search 343/726- wzg Primary Examiner-Eli Lieberman Attorney- Kenway, Jenney and Hildreth ABSTRACT: A circularly polarized broadcast antenna comprising a pair of conducting arms having portions forming an interrupted loop polarized in a first plane and terminating in ends diverging in different directions from the first plane to form a dipole.

PATENTEUAPR2H97| 3,576,567

' SHEETIUFZ FIG. "I

' FIG. 2

INVENTOR.

EDWARD H. SHIVELY BY MMaWM ATTORNEYS My invention relates to antennas, and particularly to a novel broadcast antenna especially adapted for transmitting a circularly polarized wave.

Conventional broadcast antennas have usually been arranged to produce either a vertically polarized or a horizontally polarized wave. For AM broadcasting, a vertically polarized wave has always been used. For FM and television broadcasting, it has been conventional to broadcast a horizontally polarized wave. Recently, antennas have been produced for FM and television broadcasting which include both elements for broadcasting a vertically polarized wave and other elements for radiating a horizontally polarized wave. For example, such an antenna may comprise an array of stacked V or loop antennas combined with an array of stacked vertical dipoles. With such an antenna, a broadcast wave having both vertically and horizontally polarized components is produced, contributing to better reception by randomly polarized receiving antennas. However, no attempt has been previously made to control the relative phase of the horizontally and vertically polarized components of the radiated wave. It would be highly desirable to broadcast a circularly polarized wave, comprising horizontally and vertically polarized components in fixed phase relation. It is the object of my invention to facilitate the broadcasting of circularly polarized waves.

The above and other objects of my invention are attained by an antenna construction including as the basic radiating elements a pair of conducting arms, formed intermediate their ends into an interrupted loop located in a horizontal plane. The arms are provided with a common insulated support at one end, and terminate at the other end in oppositely directed, vertically oriented elements. The radiator so formed is excited, in a manner to be described, so that the horizontal arms transmit a horizontally polarized radiation component, and the vertically disposed elements transmit a vertically polarized component. The phase relationship between the vertical and horizontal components is fixed by the geometry of the array, so that a truly circularly polarized wave, having a common center of radiation, is produced. Preferably, the vertical elements are adjustably secured to the horizontal elements so that the ratio of vertical polarization to horizontal polarization can be adjusted to compensate for variations in manufacture and to suit the antenna for use in different geographical locations. A number of such radiators may be stacked in an array, in a manner to be described, to produce a gain proportional to the number of elements. By that arrangement, an antenna is made that can, when excited by a transmitter having a given licensed power output for horizontal radiation, produce twice the total radiation available with a horizontally polarized antenna excited by the same transmitter power.

The manner in which the antenna of my invention is constructed, and its mode of operation, will be best understood from the following detailed description, together with the accompanying drawings, of a preferred embodiment thereof.

In the drawings:

FIG. 1 is a diagrammatic perspective sketch of two bays of a multiple bay antenna in accordance with a preferred embodiment of my invention;

FIG. 2 is a plan view of a radiator forming one bay of the antenna of FIG. I;

FIG. 3 is a front elevation of the radiator of FIG. 2;

FIG. 4 is a side elevation of the radiator of FIG. 2;

FIG. 5 is an enlarged cross-sectional view of a portion of the apparatus of FIG. 4, taken substantially along the lines 5-5 in FIG. 4; and

FIG. 6 is a diagrammatic perspective sketch showing the electrical characteristics of the radiator of FIGS. 2 through 5 and illustrating graphically the relationship between the currents in the various elements of the radiator during operation.

Referring to FIG. 1, a transmitting antenna in accordance with my invention may comprise any desired number of bays each formed bya radiator generally designated 1. The radiators 1 are mountedon a conducting column 3 of any desired form. In practice, I prefer to make the column 3 as a tubular metal feedline having predetermined dimensions selected in accordance with the electrical requirements of the array. Such a feedline can then be connected mechanically by conventional means to masts or towers of various dimensions. Alternatively, the column 3 may constitute both a feedline and a support for the array. i

The individual radiators 1 are spaced apart by a distance A equal to the wavelength of the carrier to be transmitted. Each of the radiators 1 comprises a mounting assembly generally indicated at 5 for mechanically securing the radiator to the column 3 and electrically connecting it to a transmission line, such as may be formed by the column 3 and a conductor centrally disposed therein.

Each of the radiators 1 comprises a loop disposed in a horizontal plane and formed intermediate the ends of a pair of conducting arms. Preferably, the portion of the arms forming the horizontal loop comprise a pair of vertically superposed, electrically interconnected conductors 7 and 9 confronting a similar pair of conductors 11 and 13.

The horizontal loop formed by thearms just described is interrupted at the backby the mounting assembly 5, and at the front by an airgap. The arms forming the loop terminate in sections extending in opposite directions out of the plane of the loop and forming a dipole. Specifically, a vertically oriented conductor 15 is electrically and mechanically connected to the conductors 7 and 9, and an oppositely direct, vertically oriented conductor 17 is connected to the end of the conductors l1 and 13.

Referring to FIGS. 2 through 5, the conductors 7, 9, 11 and 13 are formed of tubular metal, preferably stainless steel or the like. The arms 7 and 9 are bent toward the connector assembly 5 in the manner shown in FIG.v 2, and are welded or otherwise secured to a metal plate 19, preferably also of stainless steel. In a similar manner, the arms 11 and 13 are bent toward the connector assembly and welded to a metal plate 21. The plates 19 and 21 are secured by any conventional means, here shown as'by bolts 23 (FIG. 5) to a pair of opposed brackets 25 and 27, of stainless steel orthe like. The brackets 25 and 27 are 'secured to an insulating plate 29, of polytetrafluorethylene or the like, by means of bolts such as 31 and intermediate metal bearing plates 33, of stainless steel or the like. As indicated at 32, the plate 29 is formed with upstanding end portions 32 having mutually inclined upper surfaces that serve to prevent rain water from accumulating on the top of the mounting assembly.

The insulator 29 is secured to the top wall 35 of a stainless steel bracket that comprises, in addition to the top wall 35, sidewalls 37 and 39 and a backplate 41. The insulator 29 is secured to the wall 35 by any suitable means, here shown as a set of bolts such as 43 extending through a bearing plate 45 of stainless steel or the like.

The backplate 41 is secured to the column 3 by means such as the flanged connection 47 indicated in FIGS. 2 and 4. Four bolts such as 48 in FIG. 5 may be readily installed or removed to facilitate assembly and disassembly of an array. Preferably, a supplemental saddle bracket 49, bolted to the backplate 41 as indicated at 50 in FIG. 5, is provided to contribute rigidity to the mounting.

Between the. bracket 25 and the sidewall 39 is clamped an insulator 51, and between the bracket 27 and the sidewall 37 is clamped an insulator plate 53. The plates 51 and 53 may be of polytetrafluorethylene or other suitable conventional insulating material.

As indicated, the plates 51 and 53 extend beyond the plates 19 and 21 at the sides and bottom, and are formed with outwardly extending wall portions shrouding the plates 19 and 21 and those portions of the brackets 25 and 27 confronting the walls 39 and 37, respectively. This provides additional insulation between the confronting conducting plates separated by the insulators 51 and 53. The purpose is to prevent arcing or corona discharge between the plates 19 and 21 and the walls 39 and 37, respectively, while keeping the plates relatively close to the walls.

The arms 7 and 9 are secured at their outer ends, as by welding or the like, to a mounting flange 55, of stainless steel or the like. The flange 55 is secured by adjustable means, here shown as a bolt 57, to a cooperating flange 59. Suitable fittings, indicated at 61, are provided on the flange 59 to receive the ends of a tubular arm 15, of stainless steel or the like, forming the depending vertical element of the radiator. It will be apparent that by this arrangement the angle that the depending arm makes with the vertical can be adjusted at will by loosening the bolt 57 and rotating the flange 59 relative to the flange 55 to a desired degree. Preferably, an angular scale is inserted on one flange, and an index marked on the other, to facilitate this adjustment.

The upstanding arm 17 is formed by a tubular steel element, as is the arm 15, and is similarly connected to the arms 11 and 13 by means of flanges 63 and 65 and an adjustable bolt 67. In this manner, the angles that the elements 15 and 17 make to the vertical can be independently adjusted.

The total length or perimeter of the interrupted rectangular loop formed by theelements 7, 9, 11 and 13 is 1V2, where A is the wavelength of the carrier to be broadcast. The length of each of the vertical elements 15 and 17 is preferably about M8, so that the length of the dipole formed by them is M4 ,'when both elements are adjusted normal to the plane of the horizontal loop.

While the radiator of my invention can be excited in various ways, it is here shown as adapted to be coupled to a coaxial cable. Any other form of transmitting line, such as a waveguide or the like, could be employed if so desired.

The outer conductor of the coaxial cable, which may comprise or be connected to the column 3, is mechanically and electrically secured to the backplate 41 through the intermediate metallic connections. The inner conductor 71 passes through an insulator 73 and is connected to a stainless steel strap 75. A metal shield 77 surrounds the insulator 73 and is electrically and mechanically connected to the backplate 41 by conventional means, not shown.

The strap 75 is connected by the nuts and bolts suggested in FIG. 3, to a pair of connecting brackets 81 electrically and mechanically secured to the conductors 7 and 9. The brackets 81 are secured to the arms 7 and 9 at points in the vicinity of a current maximum, and selected to present the desired impedance to the line.

A return path for the radiator to the backplate 41, and consequently to the outer conductor of the coaxial feedline, is made through two capacitors formed by the mounting assembly. One of the capacitors is found by the sidewall 37 and the confronting face of the bracket 27..

The electrical circuit thus formed is best shown in FIG. 6, in which the electrically equivalent capacitors C1 and C2 are shown. Also shown in FIG. 6 are the relative currents flowing in the elements of the antenna when it is excited at its resonant frequency. As indicated, currents flow in opposite directions in the arms 7, 9 and 11, 13. However, currents flow in the same direction in the vertical elements 15 and 17.

The horizontally polarized components produced by the horizontal loop of the radiator 1 are in phase quadrature with the vertically polarized radiation from the vertical elements 15 and 17. This phase relation is not disturbed by adjusting the flanges to change the angles'made by the arms 15 and 17 with the vertical. However, adjusting that angle does change the ratio of horizontally polarized radiation to vertically polarized radiation. The total gain of the radiator is the same, more or less independently of the adjustment of the dipole elements, within a reasonable range of the angle 0 in FIG. 4. If the angle 0 is zero, the gain of the vertically polarized elements would equal the gain of the horizontally polarized elements. The

total power gain per radiator 1 is one. Thus, with the elements 15 and 17 adjusted to the vertical, the vertically polarized gain would be one-half and the horizontally polarized gain would be one-half. The total gain of a multiple bay antenna such as shown in FIG. 1 is essentially equal to the sum of the gains of the individual radiators 1. Thus, the total gain of the antenna section shown in FIG. I would be 2.

The antenna of my invention has a radiation pattern that is essentially uniform in azimuth for both horizontally and vertically polarized components. The power is largely propagated in a horizontal plane, and very little is propagated towards the zenith. Thus, the elevation pattern of both components approximates that of a vertical dipole, and the combined radiation is circularly polarized and primarily horizontally directed.

It is highly desirable in a transmitting radiator to have a relatively low value of Q. The use of a rectangular loop as the horizontal component of the radiator lowers the radiation resistance, relative to that, for example, of a truncated v antenna. Thus, the Q tends to be high. Desirably, the value of Q is I less than 20.

One approach to the problem of an unduly high Q would be to increase the dimensions of the horizontal loop. However, that would bring the radiator out of resonance. To accomplish the same purpose, in the antenna of my invention the back portion of the loop is interrupted by the capacitor formed between the mounting plates 19 and 21 and the mounting bracket so that each arm of the loop resonants in a half-wave, open circuited ends mode. The manner in which the capacitors are constructed also provides mechanical support for the arms.

Various electrical modifications in the apparatus of my invention can be made without departing from the scope of my invention in its broader aspects. For example, rather than using the capacitors C1 and C2 in FIG. 6, the two ends of the loop formed by the conductors 7, 9 and ll, 13 could be connected to an open wire transmission line approximately a quarter of a wavelength long and shorted at the opposite end. The coaxial transmission line could be tapped across this open line near the short to achieve a terminated impedance. By moving the tap point, a variety of impedancies can be presented to the transmission line. Rather than the magnetic loop coupling provided by the strap 75, the inner end of the coaxial cable could be coupled by a capacitor through one side of the loop at a point near a voltage maximum, or to one side of one of the capacitors Cl and C2.

The Q of the preferred embodiment of the antenna of my invention here described is approximately 10, a value low enough so that the effects of water drops, fog and the like are negligible. However, where icing conditions may be encountered, a provision for deicing is necessary. Referring to FIGS. 2 through 5, the apparatus of my invention is provided with an electrical deicer supplied with power by a pair of electrical leads 83 and 85 brought up to a junction box 87. The junction box is fastened in any conventional way, not shown, to the backplate 41. The leads 83 and 85 are connected to the midpoints of an endless loop 89 of resistance heating elements. The right side 91 of the loop 89 passes out through a stainless steel tube 93 welded or otherwise secured to a flange 95. The flange 95 is secured to the wall of the junction box 87, by bolts or the like. The tube 95 is joined to the tube 9, as by welding or the like, at a point that is at radio frequency ground. Such a point is located approximately halfway across the side of the loop. It is desirable to bring the heating leads in at this point, to avoid the application of a large RF voltage to them.

The right half of the loop 91 passes in the manner suggested in FIG. 5 through all of the tubing forming the various components of the side of the radiator formed by the arms 7, 9 and 15. An internal recess is provided in the flanges 55 and 57 to permit the passage of the heating leads into the tube 15.

The left side 97 of the heater loop 85 in FIG. 5 similarly passes through the arms ll, 13 and 17. In that manner, electrical heating of the entire array can be provided without expos- While I have described the apparatus of my invention with respect to the, details of a preferred embodiment thereof,

many changes and variations will occur to'those skilled in the art upon reading my description, and such can obviously be nected to the mast, a pair of conducting arms each connected at one end to said insulating means, said arms being formed intermediate their ends into a horizontally radiating loop section in a plane normal to the mast, said horizontally radiating section having a perimeter of approximately A/2 and being interrupted by the insulating means and by a gap between the arms on the side of the loop opposite the insulating means, said arms terminating in sections extending from said plane in opposite directions to form a dipole approximately A14 in length, and means for coupling said transmission line to said arms.

2. An electromagnetic radiator resonant at a wavelength A and comprising an insulating support and a pair of conducting arms each connected at one end to said insulating support, said arms being formed intermediate their ends into an interrupted loop in a first plane, said loop having a perimeter of approximately A/2 and comprising a first pair of parallel sides, one interrupted by said insulating support and the other interrupted by a gap between the anus, said loop comprising a second pair of parallel conducting sides, said arms terminating in sections extending out of said first plane in difierent directions in parallel planes normal to said first plane to form a dipole approximately AM in length.

3. An antenna resonant at a wavelength A and comprising a conducting backplate, a first pair of conducting plates electrically and mechanically connected to the backplate and extending normal to the backplate in spaced parallel relation, an insulator mounted on the backplate, a second pair of conducting plates, each of said second pair of plates being mounted on the insulator in spaced parallel confronting relation to a different one of the first pair of plates to form two capacitors having a common terminal formed by the backplate, and a pair of conducting arms each electrically and mechanically connected at one end to a different one of said second pair of plates, said arms being formed intermediate their ends into an interrupted loop in a first plane, said loop having a perimeter of approximately A12, and being interrupted by said capacitor and by a gap between the arms, said arms terminating in sections extending from the loop at said gap in difierent directions parallel to a second plane normal to said first plane to form a dipole.

4. The antenna of claim 3, in which the portions of the arms fonning the interrupted loop each comprise a pair of parallel conductors shunted at their ends and disposed in a surface normal to said first plane, and the portions of the arms forming the dipole each comprise a pair of parallel conductors shunted at their ends and disposed in planes parallel to said second plane.

5. The antenna of claim 4, further comprising a tubular conducting shield electrically and mechanically connected to said backplate, forming a passage through said backplate, and protruding toward said gap in the plane of said loop, a metal conductor extending through said shield, insulating means for supporting said metal conductor in said shield in insulated relation to said shield, means for electrically connecting said metal conductor to a point on one of said arms in said first plane, whereby said antenna will resonate and transmit radiation in response to alternating voltage having the wavelength A applied between said metal conductor and said backplate.

6. The antenna of claim 4, in which each conductor of each of said pairs of parallel conductors comprises a hollow metal tube, and further comprising means on each arm forming passages between the tubes forming the loo and the tubes orrnrng the dipole, a pair of hollow metal ubes each connected between the backplate and a different one of the arms, the connections between the last recited tubes and the arms eachbeing a connection forming a communicating passage into one of the tubes forming the loop at a point on one of said second pair of parallel sides, and electrical heating means extending through all of said tubes and terminating at common energization terminals insulated from and adjacent to said bac'kplate.

7. An antenna for operation at the wavelength A, comprising insulating means, a pair of conducting arms each connected to said insulating means and fomred intermediate its ends into an interrupted loop in a first plane, said loop having a perimeter of approximately A/2, said loop being interrupted on one side by said insulating means and on an opposite side by a gap between the arms in said first plane, said arms terminating in sections of equal length extending from said first plane in different directions parallel to a second plane normal to said first plane to form a dipole, each of said sections being approximately A/8 long.

8. The antenna of claim 7, further comprising a pair of capacitors connected in series between the ends of said arms connected to said insulating means, and means for applying a radio frequency voltage from a transmission line between the junction of said capacitors and a point on one arm in said loop.

9. The antenna of claim 7, in which the portions of said arms forming said dipole are adjustably connected to the portions of said arms forming said loop for rotation in arcs parallel to said second plane, and further comprising means connected to each arm for securing it in its adjusted position.

10. The antenna of claim 7, in which the portion of said arms forming the loop each comprise a pair of parallelconductors shunted at their ends and disposed in a surface normal to said second plane, and in which the portions of said arms forming said dipole each comprise a pair of parallel conductors shunted at their ends and disposed in a plane parallel to said second plane. 

1. A broadcast antenna for radiating a circularly polarized wave, said antenna being resonant at a wavelength lambda and comprising a conducting mast, a plurality of radiators mounted on said mast at intervals lambda , and a transmission line coupled to said radiators, each radiator comprising insulating means connected to the mast, a pair of conducting arms each connected at one end to said insulating means, said arms being formed intermediate their ends into a horizontally radiating loop section in a plane normal to the mast, said horizontally radiating section having a perimeter of approximately lambda /2 and being interrupted by the insulating means and by a gap between the arms on the side of the loop opposite the insulating means, said arms terminating in sections extending from said plane in opposite directions to form a dipole approximately lambda /4 in length, and means for coupling said transmission line to said arms.
 2. An electromagnetic radiator resonant at a wavelength lambda and comprising an insulating support and a pair of conducting arms each connected at one end to said insulating support, said arms being formed intermediate their ends into an interrupted loop in a first plane, said loop having a perimeter of approximately lambda /2 and comprising a first pair of parallel sides, one interrupted by said insulating support and the other interrupted by a gap between the arms, said loop comprising a second pair of parallel conducting sides, said arms terminating in sections extending out of said first plane in different directions in parallel planes normal to said first plane to form a dipole approximately lambda /4 in length.
 3. An antenna resonant at a wavelength lambda and comprising a conducting backplate, a first pair of conducting plates electrically and mechAnically connected to the backplate and extending normal to the backplate in spaced parallel relation, an insulator mounted on the backplate, a second pair of conducting plates, each of said second pair of plates being mounted on the insulator in spaced parallel confronting relation to a different one of the first pair of plates to form two capacitors having a common terminal formed by the backplate, and a pair of conducting arms each electrically and mechanically connected at one end to a different one of said second pair of plates, said arms being formed intermediate their ends into an interrupted loop in a first plane, said loop having a perimeter of approximately lambda /2, and being interrupted by said capacitor and by a gap between the arms, said arms terminating in sections extending from the loop at said gap in different directions parallel to a second plane normal to said first plane to form a dipole.
 4. The antenna of claim 3, in which the portions of the arms forming the interrupted loop each comprise a pair of parallel conductors shunted at their ends and disposed in a surface normal to said first plane, and the portions of the arms forming the dipole each comprise a pair of parallel conductors shunted at their ends and disposed in planes parallel to said second plane.
 5. The antenna of claim 4, further comprising a tubular conducting shield electrically and mechanically connected to said backplate, forming a passage through said backplate, and protruding toward said gap in the plane of said loop, a metal conductor extending through said shield, insulating means for supporting said metal conductor in said shield in insulated relation to said shield, means for electrically connecting said metal conductor to a point on one of said arms in said first plane, whereby said antenna will resonate and transmit radiation in response to alternating voltage having the wavelength lambda applied between said metal conductor and said backplate.
 6. The antenna of claim 4, in which each conductor of each of said pairs of parallel conductors comprises a hollow metal tube, and further comprising means on each arm forming passages between the tubes forming the loop and the tubes forming the dipole, a pair of hollow metal tubes each connected between the backplate and a different one of the arms, the connections between the last recited tubes and the arms each being a connection forming a communicating passage into one of the tubes forming the loop at a point on one of said second pair of parallel sides, and electrical heating means extending through all of said tubes and terminating at common energization terminals insulated from and adjacent to said backplate.
 7. An antenna for operation at the wavelength lambda , comprising insulating means, a pair of conducting arms each connected to said insulating means and formed intermediate its ends into an interrupted loop in a first plane, said loop having a perimeter of approximately lambda /2, said loop being interrupted on one side by said insulating means and on an opposite side by a gap between the arms in said first plane, said arms terminating in sections of equal length extending from said first plane in different directions parallel to a second plane normal to said first plane to form a dipole, each of said sections being approximately lambda /8 long.
 8. The antenna of claim 7, further comprising a pair of capacitors connected in series between the ends of said arms connected to said insulating means, and means for applying a radio frequency voltage from a transmission line between the junction of said capacitors and a point on one arm in said loop.
 9. The antenna of claim 7, in which the portions of said arms forming said dipole are adjustably connected to the portions of said arms forming said loop for rotation in arcs parallel to said second plane, and further comprising means connected to each arm for securing it in its adjusted position.
 10. The antenna of claim 7, in which the portion of said arms Forming the loop each comprise a pair of parallel conductors shunted at their ends and disposed in a surface normal to said second plane, and in which the portions of said arms forming said dipole each comprise a pair of parallel conductors shunted at their ends and disposed in a plane parallel to said second plane. 